An exemplary embodiment of this application relates to an ink jet printer having a printhead and controller that enables high-quality printing. More particularly, the exemplary embodiment relates to an ink jet printer with a set of two printhead arrays in which the second array of nozzles is movable with respect to a first array of nozzles in a cross process direction with the individual nozzles in one array being positioned in alignment or close to alignment with corresponding nozzles in the second array in the scanning or process direction.
Droplet-on-demand ink jet printing systems eject ink droplets from printhead nozzles in response to pressure pulses generated within the printhead by either piezoelectric devices or thermal transducers, such as resistors. The ejected ink droplets are propelled to specific locations on a recording medium, commonly referred to as pixels, where each ink droplet forms a spot on the recording medium. The printheads contain ink in a plurality of channels, usually one channel for each nozzle, which interconnect an ink reservoir in the printhead with the nozzles.
In a thermal ink jet printing system, for which the exemplary embodiment of this application is an example, the pressure pulse is produced by applying an electrical current pulse to a resistor typically associated with each one of the channels. Each resistor is individually addressable to heat and momentarily vaporize the ink in contact therewith. As a voltage pulse is applied across a selected resistor, a temporary vapor bubble grows and collapses in the associated channel, thereby displacing a quantity of ink from the channel so that it bulges through the channel nozzle. The ink bulging through the nozzle is ejected from the nozzle as a droplet during the bubble collapse on the resistor. The ejected droplet is then propelled to a recording medium. When the ink droplet hits the targeted pixel on the recording medium, the ink droplet forms a spot thereon. The channel from which the ink droplet was ejected is then refilled by capillary action, which, in turn, draws ink from an ink supply container.
In a typical piezoelectric ink jet printing system, the pressure pulses that eject ink droplets are produced by applying an electric pulse to the piezoelectric devices, one of which is typically located within each one of the ink channels. Each piezoelectric device is individually addressable to cause it to bend or deform and pressurize the volume of ink in contact therewith. As a voltage pulse is applied to a selected piezoelectric device, a quantity of ink is displaced from the ink channel and a droplet of ink is mechanically ejected from the nozzle associated with each piezoelectric device. Just as in thermal ink jet printing, the ejected droplet is propelled to a pixel target on a recording medium. The channel from which the ink droplet was ejected is refilled by capillary action from an ink supply. For an example of a piezoelectric ink jet printer, refer to U.S. Pat. No. 3,946,398.
A thermal ink jet printhead can include one or more printhead die assemblies, each having a heater portion and a channel portion. The channel portion includes an array of ink channels that bring ink into contact with the bubble-generating resistors, which are correspondingly arranged on the heater portion. In addition, the heater portion may also have integrated addressing electronics and driver transistors. The array of channels in a single die assembly is not sufficient to cover the full width of a page of recording medium, such as, for example, a standard sheet of paper. Therefore, a printhead having only one die assembly is scanned across the page of recording medium while the recording medium is held stationary and then the recording medium is advanced between scans. Alternatively, multiple die assemblies may be butted together to produce a full width printhead, such as, for example, the printhead disclosed in U.S. Pat. No. 4,829,324 and U.S. Pat. No. 5,221,397.
The ink jet printhead may be incorporated into a carriage type printer or a full width array type printer. The carriage type printer may have a printhead having a single die assembly or several die assemblies abutted together for a partial width size printhead. Since both single die and multiple die, partial width printheads function substantially the same way in a carriage type printer, only the printer with a single die printhead will be discussed. The only difference, of course, is that the partial width size printhead will print a larger swath of information. The single die printhead, containing the ink channels and nozzles, can be sealingly attached to a disposable ink supply cartridge, and the combined printhead and cartridge assembly is replaceably attached to a carriage that is reciprocated to print one swath of information at a time, while the recording medium is held stationary. Each swath of information is equal to the height of the column of nozzles in the printhead. After a swath is printed, the recording medium is stepped a distance at most equal to the height of the printed swath, so that the next printed swath is contiguous or overlaps with the previously printed swath. This procedure is repeated until the entire image is printed.
In contrast, the page width printer includes a stationary printhead having a length sufficient to print across the width of sheet of recording medium. The recording medium is continually moved past the full width printhead in a direction substantially normal to the printhead length and at a constant or varying speed during the printing process. Another example of a full width array printer is described, for example, in U.S. Pat. No. 5,192,959.
Ink jet printing systems typically eject ink droplets based on information received from an information output device, such as, a personal computer. Typically, this received information is in the form of a raster, such as, for example, a full page bitmap or in the form of an image written in a page description language. The raster includes a series of scan lines comprising bits representing individual information elements or pixels. Each scan line contains information sufficient to eject a single line of ink droplets across the recording medium in a linear fashion from one nozzle. For example, ink jet printers can print bitmap information as received or can print an image written in the page description language once it is converted to a bitmap of pixel information.
A problem with ink jet print printers is random failures of ink jet print heads due to nozzle contamination which limits their usefulness in high quality production applications. In the single-pass systems needed for high-speed production systems even weak or miss-directed jets may result in visible image defects in the form of streaks. Since these failures are unpredictable by nature, some form of regular output monitoring is needed to ensure that occurrences are detected before large portions of a job are affected. Even with such monitoring, the productivity impacts of stopping the press to change or purge heads could be significant.
The use of ink jet systems for high quality production printing applications has been very limited. Current systems typically address either lower quality applications such as direct mail/transaction documents or utilize pixel interlacing schemes with lower throughput rates (e.g., flatbeds printing signage). Web cleaners and air flow techniques have been used to minimize the amount of paper dust that comes in contact with the printheads, but the random failures of ink jet printheads still remain.